Maggie, who was born in captivity at the San Diego Zoo in 1961, showed a gradual decline in her health, as degenerative changes associated with her advanced age began to severely impact her quality of life, zoo officials said Saturday.

"From the day Maggie and Kecil were introduced to each other, staff noticed positive interactions. With her calm demeanor, Maggie engaged Kecil in play, slept with him, and when he first ventured out to his new habitat in Tropic World: Asia, she was always protective and nearby," zoo officials said.

In Maggie's absence, Kecil and a 7-year-old female orangutan are being slowly introduced to one another.

The decision to euthanize Maggie came after she began to suffer many of the same ailments seen in aging humans including arthritis, heart disease, hypothyroidism, and round cell sarcoma.